Catalytic reactions involving at least one or more liquid reactants with a solid catalyst are common. Typically, such reactions are carried out in one of several different types of reactors.
As taught in Kirk-Othmer, Volume 19, 1983 edition, pages 880-891, which is incorporated by reference herein, many reactors, configurations, and designs have evolved over the years. The specific reactor selection is based on the physical properties of each of the feeds to the reactor and to each of the products from the reactor, i.e. vapor, liquid, solid, or combinations; the characteristics of the chemical reactions to be carried out in the reactor, i.e. reactant concentrations, reaction rates, operating conditions, and heat addition or removal; the nature of any catalyst used, i.e. activity, life, and physical form; and the requirements for contacting reactants and removing products, i.e. flow characteristics, transport phenomena, and mixing and separating mechanisms. These factors are interdependent and must be considered together. The requirements for contacting reactants and removing products are the paramount focus of reactor technology, with the other factors usually being set by the selection of the reacting system and intended levels of reactant conversion and product selectivity.
Processes considered "high conversion" are those in which the chemical reaction approaches the point of equilibrium. One example of such a process is the isomerization of 5-vinyl-2-norbornene ("VNB") to 5-ethylidene-2-norbornene ("ENB"). ENB is used as a termonomer in the production of films for food wrap. When producing ENB, greater than 99.7% conversion is required in order to meet governmental health regulations.
Typical liquid phase reactions with solid catalysts that require high conversions (conversions approaching equilibrium) include a batch reaction with slurry catalyst, a continuous reaction in a fixed static bed reactor, or a series of continuous stirred or mixed reactors with slurry catalysts.
Fluid bed reactors, in which at least one of the reactions occurs in the gas phase, or in the liquid phase with a gas phase also present, offer the following advantages of (1) small catalyst particles can be utilized, which offer excellent mass transfer to the catalytic surface, but which are too small to practically use in a fixed bed due to high pressure drops; (2) high coefficients of heat transfer, which allow for the continuous addition or removal of heat for excellent temperature control of the reaction; and (3) catalysts can be easily added and withdrawn, either continuously or periodically, which is useful when a catalyst is used that loses activity over time and must be purged.
For example, U.S. Pat. No. 3,901,660 teaches a method to provide mixing of a heterogeneous catalyst in a fluidized bed reactor by introducing bubbles to mix the reactant together. The gas may be inert and be used simply to agitate the bed or may be non-inert and act also as a reactant.
However, such fluidized beds, which have a gas phase present, are not useful for high conversion reactions in which a close approach to equilibrium is desired, because the agitation achieved by the gas bubbles results in back-mixing of the liquid; thus, creating a mixed flow regime. Thus, the close approach to equilibrium is prevented.
Other examples of liquid phase reactions using a solid catalyst employ either mixed slurry reactors, fixed beds, or fluid beds with a gas phase also present. In all of these examples, high conversions are achieved by placing multiple mixed reactors in series, or by batch reactions, or by use of fixed bed reactors, or by use of co-current liquid/catalyst flow reactors.
There are several ways to achieve high conversion reactions, including batch reactor, a plug flow reactor, or several continuous stirred tanks. In industry, it is most pragmatic to use several continuous stirred tanks and try to put as many continuous stirred tanks to achieve plug flow as if one was using a fixed bed. When one uses a fixed bed though, one needs a solid catalyst. However, if one has a catalyst requirement that it be in a powder form, a fluidized bed is required, which therefore results in a loss of conversion rates.
It would be desirable if a process method could be developed to enable one to carry out a chemical reaction between liquid reactants using a powdered catalyst in a continuous mode of operation, without having to sacrifice conversion rates, rather than having to operate in a batch system.